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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Amino Acids

L-cysteine is a non-essential amino acid which can be synthesized in the body from L-methionine and L-serine. It is conditionally essential for pre-term infants. It is an important precursor for the synthesis of proteins such as glutathione, taurine, coenzyme A, and inorganic sulfate. L-cysteine has shown some anti-inflammatory properties and is important for the protection against various toxins.[1]

Food Sources

The following foods have the highest concentration of L-cysteine.

  • some cereals, dairy products, eggs, meat, whole grains


The following are the primary uses for L-cysteine:[1]

  • Detoxification: L-cysteine plays an important role during acetaminophen overdose. Hepatic glutathione is essential for the liver's role in detoxification; however, during acetaminophen overdose, hepatic glutathione is depleted which is life-threatening. L-cysteine via N-acetylcysteine is the antidote as it helps to restore hepatic glutathione and to prevent liver damage.
  • Osteoarthritis and rheumatoid arthritis: Due to its anti-inflammatory effects, L-cysteine has also been used to treat arthritis.

Prescribing Considerations

  • L-cysteine is available in capsules, powder, tablets, and by injection.
  • Those who supplement with L-cysteine should be sure to drink 6-8 glasses of water daily to prevent the formation of cystine renal stones. Some recommend 3-5g daily of vitamin C to aid in prevention of cystine stones.
  • Another delivery form of L-cysteine is N-acetylcysteine.
  • Only the RDA for adults has been established at 500mg - 1.5g/day. The recommended dosages varies based on age and health status. To determine what your specific requirements are talk to your naturopathic doctor or other trained medical professional.


  • General Adverse Effects: Most common side effects reported have been gastrointestinal such as nausea. Rare cases of cystine renal stone formation have been reported.
  • Children: Due to lack of long-term safety studies, supplementation should be avoided in children.
  • Pregnancy and Breastfeeding: Due to lack of long-term safety studies, supplementation should be avoided in pregnant and nursing women.
  • Contraindications: hypersensitivity to any component of the preparation; individuals prone to cystine renal stones.
  • Precautions: L-cysteine can produce a false-positive result in the nitroprusside test for ketone bodies used in diabetes.

Drug Interactions

The following are the drug interactions associated with L-Cysteine:[2]

  • Insulin - L-cysteine may inactivate insulin.
  • Monosodium Glutamate - L-cysteine may increase toxicity of monosodium glutamate (MSG) in individuals who suffer from "Chinese-restaurant syndrome". Side effects include headache, dizziness, disorientation, and burning sensation.

Nutrient Interactions

The following indicate the nutrient interactions with L-Cysteine:[1]

  • Zinc - L-cysteine complexes with zinc and may increase its absorption.
  • Vitamin C may inhibit the oxidation of L-cysteine to L-cystine.


  1. 1.0 1.1 1.2 Hendler Sheldon S., Rorvik David (Editors). PDR for Nutritional Supplements, Medical Economics Company Inc.
  2. Griffith Winter H (2000) Vitamin, Herbs, Minerals & Supplements: The Complete Guide, MJF Books